This project studies the control of expression of the 5s RNA genes (5s DNA) in the frog Xenopus. Somatic cells produce a single kind of 5s RNA, while oocytes synthesize an additional 5s species. A developmental control mechanism appears to shut off ococyte 5s DNA in somatic cells. The sequencing of unusual spacer regions in an oocyte 5s DNA clone will be completed, as will the cloning of fragments of oocyte 5s genes containing sequence variants. Assaying the capacity of such sequences to be transcribed in vitro will identify specific sites essential for transcription. The chromatin structures of oocyte and somatic 5s DNAs in liver and red cells are being compared in terms of nucleosome spacing and DNase I sensitivity. The DNA methylation patterns of the two types of 5s DNA in both tissues are being compared using restriction enzymes that are sensitive to such methylation.